Conductive member for oa equipment

ABSTRACT

It is an object of the present invention to provide a conductive member for OA equipment which shows very stable conductivity in the volume resistivity range of 10 5  to 10 12  Ω·cm, the conductivity of which is less dependent on the voltage applied and varies only slightly during continuous energization and upon changes in environmental factors such as temperature and humidity.  
     The present invention provides a conductive member for OA equipment, which is obtainable by molding a composition comprising a non-ether-based polyurethane, carbon black and bis(trifluoromethanesulfonyl)imidolithium.

TECHNICAL FIELD

[0001] The present invention relates to conductive members for OAequipment which are suitable for blades, rollers and belts for charging,developing, transfer, fixation, static electricity elimination,cleaning, paper feeding or transportation in electrophotographicapparatus and electrostatic recording apparatus such as copiers,facsimile equipment and printers.

BACKGROUND ART

[0002] OA equipment including electrophotographic apparatus andelectrostatic recording apparatus such as copiers, facsimile equipment,printers are constituted of various parts, and blades, rollers and beltsare essential parts playing such a roll as charging, developing,transfer, fixation, static electricity elimination, cleaning, paperfeeding or transportation in electrophotographic processes. These partsare mostly made of polyurethane materials and, in many cases, they mustbe provided with a conductivity of about 10⁴ to 10¹² Ω·cm from thefunctional viewpoint.

[0003] The most popular measures that has so far been taken forproviding polyurethane members for OA equipment parts with conductivitycomprises molding a polyurethane material prepared by kneading anddispersing carbon black with and in the polyol constituent, forinstance.

[0004] However, it is very difficult to provide such moldings wholly anduniformly with stable conductivity by the method comprising dispersing,by kneading, of carbon black, since a slight deviation in the amount ofaddition of such a substance, slight changes in such conditions asmaterial temperature, molding temperature and molding time and, further,the use of a different molding method result in changes in conductivepath morphology, hence in great variations in conductivity, inparticular in the volume resistivity range of 10⁶ to 10¹¹ Ω·cm.

[0005] Furthermore, carbon black is generally higher in specific gravitythan polyurethanes, so that it settles and is distributed unevenlyduring molding and, further according to the moldings morphology,leading to development of faults in conductive paths of carbon black andmaking it difficult to stably provide the moldings with uniformconductivity. This tendency is strong especially with the moldingsmolded by the centrifugal molding method in which a great centrifugalforce is exerted on the materials. Therefore, to cope with suchdifficulties, it is indispensable to strictly control the manufacturingconditions according to the moldings morphology and/or molding method.Moreover, with the conductive polyurethanes obtained by such methods,the electric resistance is highly dependent on the voltage applied,hindering the development of high-performance electrophotographicapparatus and electrostatic recording apparatus.

SUMMARY OF THE INVENTION

[0006] In view of the foregoing, it is an object of the presentinvention to provide a conductive member for OA equipment which showsvery stable conductivity in the volume resistivity range of 10⁵ to 10¹²Ω·cm, the conductivity of which is less dependent on the voltage appliedand varies only slightly during continuous energization and upon changesin environmental factors such as temperature and humidity.

[0007] The present invention is a conductive member for OA equipment,which is obtainable by molding a composition comprising anon-ether-based polyurethane, carbon black andbis(trifluoromethanesulfonyl)imidolithium.

[0008] The conductive member for OA equipment according to the presentinvention, which is a conductive blade, a conductive roller or aconductive belt also constitutes an aspect of the present invention alsoconstitutes an aspect of the present invention.

DETAILED DISCLOSURE OF THE INVENTION

[0009] In the following, the present invention is described in detail.

[0010] The present invention is concerned with a conductive member forOA equipment, which is obtainable by molding a composition comprising anon-ether-based polyurethane, carbon black andbis(trifluoromethanesulfonyl)imidolithium.

[0011] As a result of intensive investigations made by them toaccomplish the above-mentioned object, the present inventors found thatnon-ether-based polyurethanes containing carbon black andbis(trifluoromethanesulfonyl)imidolithium combinedly used as conductiveagents show very stable electric resistance in the volume resistivityrange of 10⁵ to 10¹² Ω·cm and their conductivity does not greatly dependon the voltage. These findings have now led to completion of the presentinvention.

[0012] The composition to be used the present invention comprises anon-ether-based polyurethane, carbon black andbis(trifluoromethanesulfonyl)imidolithium. The term “non-ether-basedpolyurethane” as used herein means the product of the reaction between anon-ether-based polyol and a polyisocyanate.

[0013] The above non-ether-based polyol includes, for example,condensation polymer type polyester polyols such as typicallypoly(ethylene adipate) polyol, poly(butylene adipate) polyol, andpoly(ethylene butylene adipate) polyol; lactone-derived polyesterpolyols such as typically poly(caprolactone) polyol andpoly(β-methyl-γ-valerolactone) polyol; olefin-derived polyols such astypically poly(isoprene) polyol and poly(butadiene) polyol;poly(carbonate) polyols, castor oil-based polyols, acrylic polyols,dimer acid polyols, silicone-based polyols, fluorine-containing polyols,etc.

[0014] Incidentally, ether type polyols such as typically polyethyleneglycol and poly(oxytetramethylene) glycol, are highly hygroscopic andincrease the environment dependency of the conductivity, hence areunsuited for use in producing conductive members for OA equipmentaccording to the present invention.

[0015] The above-mentioned polyisocyanate is not particularly restrictedbut includes, for example, tolylene diisocyanate (TDI),4,4′-diphenylmethanediisocyanate (MDI), liquid MDI, xylylenediisocyanate (XDI), naphthylene-1,5-diisocyanate (NDI), hexamethylenediisocyanate (HDI), hydrogenated TDI, hydrogenated MDI,isophoronediisocyanate (IPDI), lysinediisocyanate (LDI),isopropylidenebis(4-cyclohexyl isocyanate), norbornanediisocyanate andthe like.

[0016] In reacting the above non-ether-based polyol with the abovepolyisocyanate, a curing agent may be added.

[0017] The curing agent is not particularly restricted but includes, forexample, aliphatic, aromatic, alicyclic and heterocycliclow-molecular-weight glycols; triols such as trimethylolpropane andglycerin; polyhydric alcohols such as pentaerythritol and sorbitol; andamine compounds, typically methylenebis-o-chloroaniline (MOCA).

[0018] The feature of the present invention comprises in using carbonblack and bis(trifluoromethanesulfonyl)imidolithium represented by theformula shown below combinedly as conductive agents.

LiN(SO₂CF₃)₂

[0019] The above-mentioned carbon black is not particularly restrictedbut includes, for example, furnace black species such as typicallyKetjen black EC and Valcan XC-72; acetylene black, acidic carbon black,and grafted carbon species resulting from grafting of a polymer on thecarbon particle surface. These species may be used singly or two or moreof them may be used in combination.

[0020] In the present invention, carbon black is dispersed in a polyolby kneading. The amount of carbon black to be dispersed in the polyol bykneading is preferably at most 10% by weight based on the wholecomposition. When it exceeds 10% by weight, the viscosity of the polyolbecomes markedly high, making it difficult to conduct the molding and/ordehydration and defoaming procedure.

[0021] In accordance with the present invention,bis(trifluoromethanesulfonyl)imidolithium is used as a conductive agentin addition to carbon black. Bis(trifluoromethanesulfonyl)imidolithiumis preferably used in an amount within the range of 0.01 to 200% byweight relative to the amount of carbon black used in combination. Whenit is less than 0.01% by weight, the stability of conductivity will beimpaired and the variation in electric resistance value will increase.On the other hand, when it exceeds 200% by weight, no more improvementin resistance stability will be produced.

[0022] In accordance with the present invention, it has been so designedthat even when defects are produced in electronically conductive pathsof the conductive substance carbon black, the ionic conductive substancebis(trifluoromethanesulfonyl)imidolithium can complement them.Therefore, it is possible to provide the moldings with a desired levelof conductivity, irrespective of molding method and without strictlycontrolling the manufacturing conditions.

[0023] The conductive member for OA equipment according to the presentinvention is molded from the above-mentioned composition.

[0024] The above-mentioned composition comprises a non-ether-basedpolyurethane and bis(trifluoromethanesulfonyl)imidolithium andpreferably essentially consists of a non-ether-based polyurethane andbis(trifluoromethanesulfonyl)imidolithium.

[0025] In molding the above composition to obtain the conductive memberfor OA equipment, a catalyst may be added to the above composition forpromoting the curing reaction.

[0026] The catalyst is not particularly restricted but may be any of thesubstances promoting the urethane formation reaction. Thus, suchcatalysts as amine compounds and organometallic compounds, which aregenerally used in urethane formation, can be used.

[0027] The method for molding of the conductive member for OA equipmentis not particularly restricted but includes, for example, ordinarypressure casting molding, reduced pressure casting molding, centrifugalmolding, rotational molding, extrusion molding, injection molding,reaction injection molding (RIM), and spin coating.

[0028] The conductive member for OA equipment according to the presentinvention may serve as any conductive member to be used in OA equipment,without any particular restriction. As such member, there may bementioned, for example, conductive blades, conductive rollers,conductive belts and the like. Such a conductive blade, conductiveroller or conductive belt also constitutes an aspect of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0029] The present invention will be described in more detail by way ofexamples, but the present invention is not restricted only to theseexamples.

EXAMPLE 1

[0030] Poly(ethylene butylene adipate) polyol having an averagemolecular weight of 2,000 and a number of functional groups of 2 andcontaining a conductive carbon black species (Ketjen black ECP)dispersed therein by kneading as dehydrated and defoamed as a whole bywarming under reduced pressure, a prepolymer prepared by reactingpoly(ethylene butylene adipate) polyol having an average molecularweight of 2,000 and a number of functional groups of 2 with MDI toattain an NCO content of 16%, and a curing agent comprising a mixture of1,4-butanediol and trimethylolpropane in a weight ratio of 7:3 andcontaining bis(trifluoromethanesulfonyl)imidolithium dissolved thereinin advance were weighed in respective amounts such that the ratio:number of moles of the hydroxyl group in the poly(ethylene butylenesadipate) polyol with carbon black dispersed therein/number of moles ofthe isocyanato group in the prepolymer/number of moles of the hydroxylgroup in the curing agent amounted to 1:2.7:1.6 and, after mixing up ofthese with stirring, the mixture was cured in a centrifugal moldingmachine at 130° C. for about 1 hour. Then, the molding was taken out ofthe centrifugal molding machine and matured at room temperature for 12hours to give a sheet-like sample with a thickness of 2 mm. The amountof addition of bis(trifluoromethanesulfonyl)imidolithium was 70% byweight relative to that of carbon black.

EXAMPLE 2

[0031] A sample was prepared in the same manner as in Example 1 exceptthat the amount of addition of bis(trifluoromethanesulfonyl)imidolithiumwas 145% by weight relative to that of carbon black.

EXAMPLE 3

[0032] A sample was prepared in the same manner as in Example 1 exceptthat the amount of addition of bis(trifluoromethanesulfonyl)imidolithiumwas 0.2% by weight relative to that of carbon black.

EXAMPLE 4

[0033] Poly(ethylene butylene adipate) polyol having an averagemolecular weight of 2,000 and a number of functional groups of 2 andcontaining a conductive carbon black species (Ketjen black ECP)dispersed therein by kneading as dehydrated and defoamed as a whole bywarming under reduced pressure, liquid MDI as a polyisocyanatecomponent, and a curing agent comprising a mixture of 1,4-butanediol andtrimethylolpropane in a weight ratio of 7:3 and containingbis(trifluoromethanesulfonyl)imidolithium dissolved therein in advancein respective amounts such that the ratio: number of moles of thehydroxyl group in the poly(ethylene butylene adipate) polyol with carbonblack dispersed therein/number of moles of the isocyanato group in thepolyisocyanate/number of moles of the hydroxyl group in the curing agentamounted to 1:3.2:2.1 were added in a one-shot manner and, after mixingup with stirring, the mixture was cured in a centrifugal molding machineat 130° C. for about 1 hour. Then, the molding was taken out of thecentrifugal molding machine and matured at room temperature for 12 hoursto give a sheet-like sample with a thickness of 2 mm. The amount ofaddition of bis(trifluoromethanesulfonyl)imidolithium was 70% by weightrelative to that of carbon black.

EXAMPLE 5

[0034] The same compound as used in Example 1 was manually cast into amold having a 2-mm-thick spacer and maintained at 130° C. and cured atthat temperature for about 1 hour. The molding was then taken out of themold and matured at room temperature for 12 hours to give a sheet-likesample with a thickness of 2 mm.

COMPARATIVE EXAMPLE 1

[0035] Poly(ethylene butylene adipate) polyol having an averagemolecular weight of 2,000 and a number of functional groups of 2 andcontaining the same amount as used in Example 1 of a conductive carbonblack species (Ketjen black ECP) dispersed therein by kneading asdehydrated and defoamed as a whole by warming under reduced pressure, aprepolymer prepared by reacting poly(ethylene butylene adipate) polyolhaving an average molecular weight of 2,000 and a number of functionalgroups of 2 with MDI to attain an NCO content of 16%, and a curing agentcomprising a mixture of 1,4-butanediol and trimethylolpropane in aweight ratio of 7:3 were weighed in respective amounts such that theratio:number of moles of the hydroxyl group in the poly(ethylenebutylene adipate) polyol with carbon black dispersed therein/number ofmoles of the isocyanato group in the prepolymer/number of moles of thehydroxyl group in the curing agent amounted to 1:2.7:1.6 and, aftermixing up thereof with stirring, the mixture was cured in a centrifugalmolding machine at 130° C. for about 1 hour. Then, the molding was takenout of the centrifugal molding machine and matured at room temperaturefor 12 hours to give a sheet-like sample with a thickness of 2 mm.

COMPARATIVE EXAMPLE 2

[0036] A sheet-like sample with a thickness of 2 mm was obtained in thesame manner as in Comparative Example 1 except that the amount of theconductive carbon black (Ketjen black ECP) dispersed was the same as inExample 2.

COMPARATIVE EXAMPLE 3

[0037] The same compound as used in Comparative Example 1 was manuallycast into a mold having a 2-mm-thick spacer and maintained at 130° C.and cured at that temperature for about 1 hour. Then, the molding wastaken out of the mold and matured at room temperature for 12 hours togive a sheet-like sample with a thickness of 2 mm.

[0038] The samples obtained in Examples 1 to 5 and Comparative Examples1 to 3 were subjected to the following evaluation tests. The results areshown in Table 1.

[0039] [Conductivity Evaluation]

[0040] Evaluation measurements were made using a resistance measuringapparatus (model R8340A, produced by Advantest Corp.)

[0041] (1) Volume Resistivity

[0042] Each sample was evaluated for volume resistivity by applying avoltage of 250 V for 30 seconds. Measurements were made at 15 sites allover the sample surface, and the arithmetic mean was reported as thevolume resistivity value.

[0043] (2) Variation in Volume Resistivity

[0044] The volume resistivity values for the 15 sites as obtained in (1)were plotted on a logarithmic graph paper each scale mark of whichcorresponded to 1×10^(x) (x represents an integer), and the variationwas evaluated in terms of the difference, in number of scale marks,between the maximum and minimum value.

[0045] (3) Voltage Dependency

[0046] A voltage of 10 to 1,000 V was applied to each sample for 30seconds, and the volume resistivity values thus obtained were plotted ona logarithmic graph paper each scale mark of which corresponded to1×10^(x) (x represents an integer), and the dependency was evaluated interms of the difference, in number of scale marks, between the maximumand minimum value.

[0047] (4) Changes During Continuous Energization

[0048] A voltage of 100 V was applied to each sample continuously for 30seconds, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30minutes, and resistant measurements were made at 5-minute intervals. Thedata obtained were plotted on a logarithmic graph paper each scale markof which corresponded to 1×10^(x) (x represents an integer), and theevaluation was made in terms of the difference, in number of scalemarks, between the maximum and minimum value.

[0049] (5) Changes in the Environment

[0050] A voltage of 250 V was applied to each sample for 30 seconds in alow-temperature, low-humidity environment (10° C., 15% relativehumidity) to a high-temperature, high-humidity environment (32.5° C.,85% relative humidity), and the volume resistivity were measured andplotted on a logarithmic graph paper each scale mark of whichcorresponded to 1×10^(x) (x represents an integer). The evaluation wasmade in terms of the difference, in number of scale marks, between themaximum and minimum value. TABLE 1 Conductivity Volume Variation inChanges during resistivity volume Voltage continuous Changes in the (Ω ·cm) resistivity dependency energization environment Example 1 1.7 × 10⁶  3 marks  7 marks  5 marks 10 marks Example 2 1.1 × 10¹¹  2 marks  5marks  3 marks  8 marks Example 3 2.2 × 10⁸   5 marks  9 marks  6 marks11 marks Example 4 9.2 × 10⁵   4 marks  8 marks  5 marks 11 marksExample 5 1.4 × 10⁶   4 marks  7 marks  4 marks 10 marks Comparative 7.0× 10⁸  25 marks 60 marks 12 marks 30 marks Example 1 Comparative 9.4 ×10¹¹ 50 marks 60 marks 35 marks 25 marks Example 2 Comparative 4.3 ×10⁵  15 marks 30 marks 11 marks 20 marks Example 3

INDUSTRIAL APPLICABILITY

[0051] The present invention, which has the constitution describedhereinabove, can provide conductive members for OA equipment whichsimultaneously have such characteristics as very stable electricresistance in the volume resistivity range of 10⁵ to 10¹² Ω·cm, slightdependency of conductivity on voltage, and small changes in conductivityduring continuous energization and upon changes in environmental factorssuch as temperature and humidity.

1. A conductive member for OA equipment, which is obtainable by moldinga composition comprising a non-ether-based polyurethane, carbon blackand bis(trifluoromethanesulfonyl)imidolithium.
 2. The conductive memberfor OA equipment according to claim 1, which is a conductive blade. 3.The conductive member for OA equipment according to claim 1, which is aconductive roller.
 4. The conductive member for OA equipment accordingto claim 1, which is a conductive belt.